Communication devices and methods with beamforming training

ABSTRACT

A communication device, e.g. an access point, for RF-based communication with another communication device, e.g. a station, comprises antenna circuitry configured to transmit and receive RF signals and beamforming circuitry configured to perform beamforming. The beamforming circuitry controls the antenna circuitry to transmit data, in a beacon transmission phase prior to the beamforming training phase, using a set of third directive transmit beams in subsequent time slots and to listen, in the beamforming training phase, using a set of first directive receive beams in subsequent time slots that is different from the set of third directive transmit beams.

BACKGROUND Field of the Disclosure

The present disclosure relates to different communication devices, suchas a mobile station and an access point, which are configured forRF-based communication with each other. The present disclosure furtherrelates to corresponding communication methods.

Description of Related Art

Communication systems in the 60 GHz frequency range suffer from strongfree space path loss, which increases with frequency. For instance, a 60GHz communication system has roughly 22 dB higher attenuation comparedto a communication system operating at 5 GHz. To overcome the increasedpath loss, 60 GHz or any mmWave communication system employsbeamforming, i.e. transmitter and/or receiver feature a steerablephased-array antenna (PAA), which can form directive beams towards theother communication device. Such beams have typically a high directivityand are spatially very narrow. The directivity in main directionincreases with the number of antenna elements per PAA. In contrast, thehalf-power beam width (HPBW) defines the spatial width of a patterndecreases with increasing number of antennas. Thus, the more antennasper PAA, the higher the directivity and the smaller the HPBW. In orderto make use of the PAA directivity for communications, beam alignment iscrucial and of high importance for mmWave communication systems and RFcommunication systems, methods and devices in general.

Beamforming training for association is however a challenging problemdue to i) lack of any knowledge at one of the communication devices,e.g. at the access point (AP), about other communication devices, e.g.the stations (STAs), that may want to associate, and ii) relativelyscarce knowledge at STAs about the “good” sectors on which they canlisten on. The latter is due to the fact that the STAs listen generallyin quasi-omnidirectional mode. To tackle the first problem the IEEE802.11ad and 802.11ay standards have designed a specific associationbeamforming interval in which STAs randomly choose slots in which theyopportunistically send directive beams to the AP, containing informationabout their address and AP transmit beams best received during thebeacon intervals.

The problems with this approach are collision probability since APslisten omnidirectional so that frames from multiple STAs can collide,especially in dense scenarios, and coverage problems since thedirectivity gain at STAs can be significantly lower than at the AP orSTAs can be far from the APs, in which case the beams transmitted by theSTAs do not reach the APs.

There is a need in such communication systems to yield higher antennagain in an association phase, thus increasing the AP coverage andenabling long-range association and data transmission. Furthermore, itis desired to reduce the collision probability among STAs (firstcommunication devices) during association phase.

The “background” description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventor(s), to the extent it is described in thisbackground section, as well as aspects of the description which may nototherwise qualify as prior art at the time of filing, are neitherexpressly or impliedly admit-ted as prior art against the presentdisclosure.

SUMMARY

It is an object to provide communication devices and correspondingcommunication methods yielding a higher antenna gain, enablinglong-range association and data transmission, and/or reducing thecollision probability in association phase.

According to an aspect there is provided a (first) communication device,e.g. an access point, for RF-based communication with anothercommunication device, said communication device comprising:

-   -   antenna circuitry configured to transmit and receive RF signals,        and    -   beamforming circuitry configured to perform beamforming and to        perform beamforming and to control the antenna circuitry to        transmit data, in a beacon transmission phase prior to the        beamforming training phase, using a set of third directive        transmit beams in subsequent time slots and to listen, in the        beamforming training phase, using a set of first directive        receive beams in subsequent time slots that is different from        the set of third directive transmit beams.

According to a further aspect there is provided a (second) communicationdevice, e.g. a station, for RF-based communication with anothercommunication device, said communication device comprising:

-   -   antenna circuitry configured to transmit and receive RF signals,        and    -   beamforming circuitry configured to perform beamforming and to        control the antenna circuitry to transmit data using at least        one first directive transmit beam while the other communication        device is listening subsequently using different first directive        receive beams, wherein data is only transmitted in one or more        selected time slots, in which the other communication device is        listening with a selected first directive receive beam, wherein        the one or more time slots are selected based on information        received from the other communication device or derived from        third directive transmit beams used by the other communication        device to transmit data in a beacon transmission phase prior to        the beamforming training phase.

According to still further aspects corresponding communication methods,a computer program comprising program means for causing a computer tocarry out the steps of the methods disclosed herein, when said computerprogram is carried out on a computer, as well as a non-transitorycomputer-readable recording medium that stores therein a computerprogram product, which, when executed by a processor, causes the methodsdisclosed herein to be performed are provided.

Embodiments are defined in the dependent claims. It shall be understoodthat the disclosed methods, the disclosed computer program and thedisclosed computer-readable recording medium have similar and/oridentical further embodiments as the claimed devices and as defined inthe dependent claims and/or disclosed herein.

One of the aspects of the disclosure is to provide associationbeamforming training, which applies directive beams on at least thesecond communication device (AP), preferably on both communicationdevices (AP and STA). This yields an increase in link budget during theassociation phase, which can be exploited to extend association range,i.e. long range association beamforming training. Thus, firstcommunication devices being far away from the second communicationdevice can discover and join the basic service set (BSS) of that secondcommunication device. Further, it is proposed to modify channel accessduring the association beamforming training if reciprocity can beassumed. This reduces the collision probability between firstcommunication devices by exploiting their inherent spatial beamseparation.

Further, a protocol and a signaling solution are disclosed to reduce thetraining time and at the same time allow for improved coverage andreduced collision probabiity. With the disclosed approach the receivebeams utilized by the AP in the directive association phase are neitherrestricted to be the same, nor are they restricted to be in the sameorder as the transmit beams utilized in the preceding beacon traininginterval. Furthermore, embodiments of the disclosed solutions enable theAP to listen with variable beam widths during the association interval,whereby the beam widths may be chosen to cover one or more of the narrowbeams, which have been previously used in transmit sector sweeps of abeacon interval. Reductions in overhead and training time may thus beachieved as compared to state of the art methods.

In the following, the terminology of WLAN systems is used, i.e. there isa station (STA) as an example of a first communication device and asingle central network access point (AP) or personal basic service setcontrol point (PCP) (generally referred to as AP herein; WLANterminology sometimes uses the abbreviation PCP/AP) as an example of asecond communication device, wherein the first and second communicationdevices may also be called transmitter and receiver. Both communicationdevices intend to exchange data wirelessly in the 60 GHz (mmWave)frequency band. However, this invention is applicable to any other RFcommunication system employing beamforming such as mmWave LTE

The foregoing paragraphs have been provided by way of generalintroduction, and are not intended to limit the scope of the followingclaims. The described embodiments, together with further advantages,will be best understood by reference to the following detaileddescription taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING

A more complete appreciation of the disclosure and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 shows a schematic diagram of a communication system includingfirst and second communication devices;

FIG. 2 shows a diagram of a transmission interval as described inIEEE802.11ad;

FIG. 3 shows a diagram of conventional association beamforming training;

FIG. 4 shows a diagram of a beacon transmission interval;

FIG. 5 shows a diagram of a first embodiment of association beamformingtraining with a single STA;

FIG. 6 shows a diagram of a second embodiment of association beamformingtraining with a two STAs;

FIG. 7 shows a diagram of a third embodiment of association beamformingtraining with a two STAs employing reciprocity;

FIG. 8 shows a diagram of a Beacon Interval Control Field;

FIG. 9 shows a diagram of beacon frame body structure;

FIG. 10 shows a diagram of a simple association beamforming controlfield;

FIG. 11 shows a diagram of an advanced association beamforming controlfield;

FIG. 12 shows a diagram of an embodiment of a beacon transmission phaseaccording to another aspect;

FIG. 13 shows a diagram of an embodiment of association beamformingtraining according to another aspect;

FIG. 14 shows a diagram of an embodiment of an SSW field;

FIG. 15 shows a diagram of a first embodiment of a PPDU and framestructure and corresponding AWV configurations;

FIG. 16 shows a diagram of a second embodiment of a PPDU and framestructure and corresponding AWV configurations;

FIG. 17 shows a diagram of another embodiment of a beacon transmissionphase;

FIG. 18 shows a diagram of still another embodiment of a beacontransmission phase and a beamforming transmission phase;

FIG. 19 shows a diagram of an embodiment of an extended schedulingelement;

FIG. 20 shows a diagram of another embodiment of an extended schedulingelement and

FIG. 21 shows a diagram of an embodiment of an EDMG extended scheduleelement.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Referring now to the drawings, wherein like reference numerals designateidentical or corresponding parts throughout the several views, FIGS.1-11 illustrate communication devices and method according to a firstaspect of the present disclosure and FIGS. 12-18 illustratecommunication devices and methods according to a second aspect of thepresent disclosure.

FIG. 1 shows a schematic diagram of a communication system includingfirst communication devices 1, 3 (stations STA1, STA2) and a secondcommunication device 2 (an access point AP). Each of the firstcommunication devices 1, 3 comprises an antenna circuitry (sometimesalso called antenna unit) 10, 30 configured to transmit and receive RFsignals, and a beamforming circuitry (sometimes also called beamformingunit) 11, 31 configured to perform beamforming and to control itsantenna circuitry 10, 30. Similarly, the second communication devices 2comprises an antenna circuitry 20 configured to transmit and receive RFsignals, and a beamforming circuitry 21 configured to performbeamforming and to control its antenna circuitry 20. More details oftheir operation will be described below.

Communication systems in the 60 GHz frequency range suffer from strongfree space path loss a_(fs) which increases with frequency:

a _(fs)[dB]=−147.55 dB+20 log₁₀ f+20 log₁₀ d

This formula above gives the free space path loss in dB as a function offrequency f and link distance d. Apparently, a 60 GHz communicationsystem has roughly 22 dB higher attenuation compared to a communicationsystem operating at 5 GHz.

To overcome the increased path loss, 60 GHz or any mmWave communicationsystem employs beamforming, i.e. transmitter and/or receiver feature anantenna circuitry, e.g. a steerable phased-array antenna (PAA), whichcan form directive beams towards the another communication device. Suchbeams have typically a high directivity and are spatially very narrow.The directivity in main direction increases with the number of antennaelements per PAA. In contrast, the half-power beam width (HPBW) definesthe spatial width of a pattern decreases with increasing number ofantennas. Thus, the more antennas per PAA, the higher the directivityand the smaller the HPBW. In order to make use of the PAA directivityfor communications, beam alignment is crucial and of high importance formmWave communication systems.

In the following description of exemplary embodiments, the terminologyof WLAN system will be used, i.e. there is a station (STA) and a singlecentral network access point (AP) or personal basic service set controlpoint (PCP), i.e. the term AP as used herein shall be understoodgenerally to reference either an AP or a PCP (also referenced as PCT/APsometimes in WLAN terminology). Both intend to exchange data wirelesslyin e.g. the 60 GHz (mmWave) frequency band. However, this disclosure isnot limited to this frequency band, but is applicable to any othercommunication system employing beamforming such as mmWave LTE forexample.

This disclosure particularly addresses the association phase (alsocalled beamforming training phase or association beamforming trainingphase) during which STAs discover and associate to an AP. This phase isin particular challenging since initial beam aligi-ment needs to beperformed.

FIG. 2 shows a diagram of a transmission interval as described inIEEE802.11ad. The beacon interval (BI) is continuously repeated and thebeacon header interval (BHI) holds all phases with respect toassociation. The actual data transfer occurs in data transm-sioninterval (DTI). Since it is desired to keep DTI long compared to theBHI, the association beamforming training (A-BFT) phase and theannouncement transmission interval (ATI) in BHI can be occasionallyturned off, which is indicated in beacon frames sent during BTI.

Generally, according to IEEE802.11ad during a beacon transmissioninterval (BTI), the AP transmits identification data over variousdirective beams which have their main directivity in different spatialdirections. An STA listens to the medium, e.g. with an (quasi)omni-directional (also called “quasi-omni” hereinafter) or wide beamantenna, i.e. no directive pattern is applied. Once a STA receives theAP identification data, it remembers the sector ID which has beenapplied for this message. Furthermore, it (e.g. randomly) chooses a timeslot to transmit in the opposite direction (STA->AP) during associationbeamforming training (A-BFT) phase which follows subsequently to theBTI. In A-BFT, the STA transmits data with various directive beams tothe AP, which listens with an (quasi) omni-directional antenna. The STAtransmit data holds the best sector ID of the previous BTI. When the STAstops transmitting and the AP successfully received at least onemessage, the AP confirms reception including the STA sector which wasreceived in best quality (e.g. highest SNR). This message is transmittedvia the beam corresponding to the best sector ID indicated in previousA-BFT phase. The actual association procedure takes place in thefollowing announcement transmission interval (ATI). In the ATI, the bestbeams indicated by best sector IDs of BTI and A-BFT are employed.

In A-BFT, several STAs can compete for channel access. Therefore, theA-BFT is split in several slots as depicted in FIG. 3, which shows adiagram of conventional association beamforming training. Here, theA-BFT is exemplarily split in 4 slots where STAs can respond. STAs whichwould like to associate with the AP choose randomly a single slot. Thisreduces the likelihood of a collision. In case a collision happens, theAP is able to detect and it avoids sending the SSW feedback frame whichis a reception confirmation. In case the SSW feedback is sent, it holdsinformation about the best transmit sector ID of the STA. STAs notreceiving the SSW feedback choose randomly a further A-BFT slot whichcould be even in an upcoming BI. The actual sweep of different antennasectors within a single A-BFT slot is done in the SSW frames. Each SSWframe is transmitted with a distinct antenna sector which has a sectorID label indicated within the same SSW frame.

The above described operation has the drawback that association happensin directive-to-omni (D2O) mode which allows for less antenna gaincompared to a directive-to-directive (D2D) mode. Hence, according to thepresent disclosure an association phase employing D2D yielding higherantenna gain in association phase is employed, thus increasing the APcoverage and enabling long range association and data transmission.Furthermore, double directive beamforming allows for spatial reuseduring the association phase which can be exploited to reduce collisionprobability among STAs during association phase.

FIG. 4 depicts a diagram of several beacon transmission intervals (BTI)according to an aspect of this disclosure, i.e. shows the AP TX and STARX training procedure (also called beacon transmission phase) assumingthat the STA has N different receive patterns which it intends to train.Each DMG (directional multi-gigabit) beacon frame that is transmitted ina BTI uses a dedicated direction or sector (i.e. a dedicated transmitbeam, also referred to as “third directive transmit beam” herein), whichis signaled within the DMG beacon. Thus, a STA receiving a DMG beaconcan retrieve the TX sector ID the AP used to transmit this particularbeacon.

The first step of the operation in the BTI described above may remainunchanged at the AP side, i.e. the AP transmits identification data viavarious directive beams 40 (“third directive transmit beams”). Incontrast to the known operation as described above, a STA listens withvarious directive receive beams 50 (“third directive receive beams”).Since the STA is not aligned to the frame structure at this point, a STAmay apply its directive receive beam 50 for the duration of at least onebeacon interval (BI). During the BI, the receive pattern shall beunchanged. The IEEE802.11ad standard defines the maximum duration of aBI up to 1000 ms, typical values are in the range of 100 ms. A STAlistens continuously to the channel and applies thereby its directivereceive patterns successively. After all directive receive patterns havebeen applied, either an AP has been detected (case A) or no AP has beendetected (case B).

In case A, the STA intends to communicate in a double directive A-BFT(DD-A-BFT) phase and the STA saves the best AP transmit sector (e.g. as“second transmit beam information”, also referred to as TX_(AP)) andbest STA receive sector (e.g. as “second receive beam information”, alsoreferred to as RX_(STA)) The best sector can be determined by evaluatingSNR, SINR, or link capacity for example.

A STA should only consider communicating within a DD-A-BFT underspecific conditions: e.g., if (i) the received SNR with sectors TX_(AP)and RX_(STA) is below a threshold, or (ii) the data reception inprevious BTI was not successful with a quasi-omni pattern, or (iii) thenumber of FailedRSSAttempts (number of unsuccessful associationattempts) in regular A-BFT with quasi-omni pattern is above a threshold,or (iv) too many collisions arise in regular A-BFT triggering the needfor spatial reuse in association phase. If the SNR is above thisthreshold, a STA shall consider a regular A-BFT. The threshold value indB may be defined by

γ_(target) +D _(STA,RX) +D _(AP,TX) −D _(STA,TX) −D _(AP,RX)

Thereby, γ_(target) denotes the target SNR of the Control PHY MCS in dB,which is the most robust modulation coding scheme (MCS) and which isapplied in beamforming training. Furthermore, DD denotes the beamdirectivity in dB of either STA or AP in either TX or RX mode,respectively.

In case B, no AP has been detected and the STA may repeat the listingprocedure with various directive beams continuously or at a later pointin time.

It should be noted that the AP may perform no special operations duringthis training phase. The modifications are mainly on STA side.Therefore, this approach can reuse any BTI such as described inIEEE802.11ad and/or IEEE802.11ay BTI. No dedicated double directive orlong range BTI is required. Given that spatial reuse is the mainobjective of a STA, it may receive with an omni-directional patternduring a single BTI phase like it is done according to IEEE802.11ad.Prerequisite is that the link budget is sufficient to overcome pathloss.

In a second phase (also called association beamforming training phase),the STA TX and AP RX procedure takes place in various DD-A-BFT slots.During a single DD-A-BFT slot, the STA uses different transmit sectors,one for each SSW frame. The AP keeps its receiver pattern unchangedduring an entire DD-A-BFT slot, i.e. each SSW frame transmitted by theSTA within one DD-A-BFT slot shall be received by the AP with the samereceive beam or RX sector, respectively. Each DD-A-BFT slot usesdifferent AP receiver patterns. In contrast to known procedures, a STAtransmits SSW frames in all DD-A-BFT slots in order to cover allpossible beam combinations.

In case of reciprocity, the channel, the applied beams, and the antennasare independent and invariant with respect to the communicationdirection, i.e. TX and RX beams have same properties and are similar inpoint of main lobe directivity and HPBW; location of side lobes is notimportant as long as the side lobe attenuation is large enough). Channelreciprocity is a prerequisite for having beam and/or antenna reciprocitywhich is an implementation property. For this reason, beam and/orantenna reciprocity can be either on STA and/or AP side or it is notavailable at all, i.e. this property is device specific. In order tokeep the notation simple, the term reciprocity is used in the following.In case of single antenna systems, reciprocity includes channel and beamreciprocity. In case of multi-antenna systems antenna reciprocity is anadditional prerequisite.

First, the case shall be considered where reciprocity is availableneither at AP nor at STA side. FIG. 5 shows a diagram of a firstembodiment of association beamforming training with a single STA. Ineach of the DD-A-BFT slots, the AP listens with a directive beam 60, 62,respectively (“first directive receive beam”). Each DD-A-BFT slot mayhave a different beam 60, 62 (it may be beneficial to use same receivebeam in various DD-A-BFT slots, as will be explained later).

The STA is transmitting several SSW frames within one or more A-BFTslots, starting from the first A-BFT slot of the DD-A-BFT. In eachDD-A-BFT slot, a STA can sweep through M different transmit patterns,i.e. use different directive beams 70 (“first directive transmitbeams”). Thereby each SSW frame holds information about the bestreceived AP transmit sector (TX_(AP), “second transmit beaminformation”) determined in the BTI phase (see FIG. 4) and the currenttransmit sector of the STA. In order to receive the SSW feedback(“response”), a STA uses its best RX beam 71 as indicated by RX_(STA)(“second receive beam information”) determined earlier in the BTI phase.

The number of slots N and the number M of SSW frames per slot may besignaled in the beacon interval control field (see below) and determinedby the AP. In case a STA stp-ports less than M transmit sectors, itshall stop transmission within the current slot after having completedall its transmit patterns and continue in the next DD-A-BFT slot ifnecessary. In case a STA supports more than M transmit sectors, it shalltransmit only M selected sectors within a slot. The selection procedureis STA specific and may comprise an angular interpolation betweenavailable sectors.

In terms of the SSW feedback, the following rules are preferably appliedin an embodiment:

1. If the AP was able to decode a SSW frame sent by a STA, it transmitsa SSW feedback (“response”), preferably with TX sector information datacontained in the SSW frame (TX_(STA), “first transmit beam information”)and using a directive transmit beam 61 indicated by TX_(AP) (“secondtransmit beam information”).

2. A SSW feedback is not sent if there has been no decodable SSW frameor if several STAs have been received simultaneously (collision). Acollision is defined as a SSW frame received from at least two STAssimultaneously. More than one valid SSW frame reception from more thanone STAs within a DD-A-BFT slot is not considered to be a collision butas feedback congestion. It shall be noted that some standards define acollision as two STAs using the same A-BFT slot even though the STAsaccess different SSW frames.

3. In case more than one SSW frames from more than one different STAshave been received during a DD-A-BFT slot (feedback congestion), the SSWfeedback is addressed to the strongest STA. Pending SSW feedbacks may beaddressed in future DD-A-BFT slots within same DD-A-BFT. In this casethe same rule of sending the SSW feedback to the strongest STA applies.At the end of a DD-A-BFT phase, all pending SSW feedbacks shall beneglected.

4. In case a STA received a SSW feedback, it stops transmitting infurther DD-A-BFT slots within the current BTI. This is to ensure thatDD-A-BFT slots can be used for further stations to associate.

5. In case a STA received no feedback it schedules transmission in afurther DD-A-BFT slot but keeps listening to the channel during all SSWfeedback phases of same DD-A-BFT phase. This is to ensure that a STA canreceive a SSW feedback frame at a later point in time in case offeedback congestion.

In FIG. 5 it is assumed that the AP receives a valid SSW frame in theN^(th) DD-A-BFT slot. Therefore, there is only one SSW feedback sent atthe end of the N^(th) DD-A-BFT slot.

In contrast to known operations, where STAs choose randomly a singleA-BFT slot for doing their sector sweep (in case a STA cannot finish itssector sweep, it may continue in the next slot), STAs transmit in someembodiments from the beginning of the first DD-A-BFT slot. Thelikelihood of a collision is reduced by the fact that the AP usesdirective receive beams, instead of an omni-directional pattern. Acollision arises if within one SSW frame interval of one DD-A-BFT slotsignals from two or more STAs have been received with similar power.Since the AP applies directive receive patterns, collision probabilityis lower compared to quasi-omni reception.

The above rule 3 applies, if the AP received more than one valid SSWframe from more than one STA. Because two frames have not been receivedat the same time, it is not a collision. At this point, the AP shouldsend two SSW feedbacks which may be not possible (as in IEEE 802.11adspecification) leading to feedback congestion which reeds to beresolved. Therefore, the AP transmits to the STA received strongest (interms of SNR, SINR, or capacity for example) and the AP uses one of theupcoming SSW feedback opportunities to address the weak STA.Alternatively, frame structures to allow for simul-taneous feedback tomultiple STAs can be envisioned. In this case, the SSW feedback may besent simultaneously to all or a set of the STAs that were receivedwithin the same DD-A-BFT slot.

FIG. 6 shows a diagram of a second embodiment of association beamformingtraining with a two STAs associating simultaneously. It is assumed thatSTA 1 and STA 2 have been able to associate in the first and secondDD-A-BFT slot, respectively. If a SSW feedback has been received, bothAP and STAs have knowledge of the best TX and RX sector ID to use forsubsequent communications. Note that only TX sector information isrequired to be exchanged between AP and STA during SSW frames and SSWfeedback, respectively.

In the example shown in FIG. 6, in a first sector sweep STA1 uses firstdirective transmit beams 70, STA2 uses first directive transmit beams 80and AP listens using a first directive receive beam 60. Preferably, inthe first directive transmit beams 70 and 80 the information about thebest third transmit beam used by the AP in the beacon transmissioninterval for the respective STA (i.e. TX_(AP)(STA1) and TX_(AP)(STA2),“second transmit beam information”) is included.

If during the first sweep the AP received a valid SSW frame only fromSTA1, it sends a SSW feedback (“response”) that is addressed to STA1using a second directive transmit beam 61 indicated by the secondtransmit beam information TX_(AP)(STA1) from STA1. Simultaneously, STA1and STA2 listen with the respective second directive receive beam 71, 81indicated by the second receive beam information RX_(STA1) andRX_(STA2). Since the SSW feedback is addressed to STA1, e.g. byincluding a corresponding identifier such as MAC address, AID(association identifier), or pre-AID, STA1 now knows its best sector(i.e. its best directive transmit beam) to use for subsequentcommunication since this information is included in the SSW feedbacktransmitted with 61. STA1 can now stop transmitting SSW frames insubsequent slots.

Subsequently, in a second sector sweep, STA2 uses first directivetransmit beams 80 AP listens using a first directive receive beam 62. Ifthe AP received a valid SSW frame from STA2 it sends a SSW feedback(“response”) that is addressed to STA2 and uses a second directivetransmit beam 63 indicated by the second transmit beam informationTX_(AP)(STA2) from STA2. Simultaneously, STA2 listens with therespective second directive receive beam 81 indicated by the secondreceive beam information RX_(STA2). Since the SSW feedback is addressedto STA2, e.g. by including a corresponding identifier, STA2 now knowsits best sector (i.e. its best directive transmit beam) to use forsubsequent communication since this information is included in the SSWfeedback 63. STA2 can now stop transmitting SSW frames in subsequentslots.

FIG. 7 shows a diagram of a third embodiment of association beamformingtraining with two STAs employing reciprocity. In this case, a STA hasalready the information about its best TX beam namely the best RX beam,i.e. TX_(STA)=RX_(STA) (equal sign should be inter-preted as describedabove). In this case, a STA transmits randomly only one SSW frame withineach DD-A-BFT slot using TX_(STA)=RX_(STA). This is to vacate theDD-A-BFT slots for other STAs competing for association in the same BI.FIG. 7 shows the basic procedure for two STAs (no collision or feedbackcongestion assumed). Dashed SSW frames indicate frames that are nottransmitted but are virtual placeholders (SSW frame transmitopportunities).

Furthermore, if it is known by the STA when the AP uses a particularreceived pattern and if the AP features reciprocity, it transmits onlyone SSW frame in each DD-A-BFT slot where the AP receives with thedesired receive beam. Since the STA knows best TX_(AP) sector, it isalso aware of the best RX_(AP) sector (TX_(AP)=RX_(AP)). If the sweepsequence of TX and RX beams is equal, the STA can predict, when the APapplies the appropriate receive pattern in DD-A-BFT. Alternatively, theRx sectors, which the AP is going to use in DD-A-BFT, can be signaledwithin the DMG beacon. In this case, a single STA can occupy randomlyeven only one SSW slot within all DD-A-BFT slots during a BI. However,for more robustness, a single STA can occupy several SSW slots in orderto train more (e.g. neighboring) RX sectors at AP and/or it can use moreSSW frames within a slot in order to train more of its own TX sectors(e.g. TX sectors that are neighbors of the RX sectors on which thehighest SNR was received during the AP SSW in BTI).

If the AP features reciprocity but the STA does not, a STA transmitsonly in that single slot where the AP applies the appropriate receivesector, i.e. RX_(AP)=TX_(AP). This requires the STA to be aware in whichslot the AP applies a dedicated receive sector.

It should be noted that all four variants—no reciprocity, STAreciprocity, AP reciprocity, AP and STA reciprocity—can be appliedindependently and simultaneously. There is no requirement that allassociating STAs have same properties or access rules

In current IEEE 802.11ad specification, an AP supports only around-trip-time delay of 1 μs, which corresponds to a maximum range of150 m. It is proposed to change this value to multiples of 1 μs usinge.g. the “Coverage Class field” as defined in the IEEE 802.11 standard.At the moment this field is not applicable for mmWave communication.

All variable parameters may be signaled in the Beacon Interval Controlfield shown in FIG. 8, which is part of DMG beacon frame body. Forexample: A-BFT length field indicates the number of A-BFT slots (1 up to8); FSS indicates the number of SSW frame slots within one A-BFT slot (1up to 16); Next A-BFT field indicates the number of BI during which theA-BFT is not present; N BIs A-BFT field indicates the interval, innumber of beacon intervals, at which the AP allocates an A-BFT. Allother fields are described the IEEE 802.11 standard.

For DD-A-BFT, the minimal change required is an indication if theupcoming A-BFT is a DD-A-BFT. It is proposed to use a single bit of thereserved bits (B44 to B47 in FIG. 8) to indicate a DD-A-BFT.

A further option to signal a DD-A-BFT is to add a further control fieldin the DMG beacon frame body shown in FIG. 9. The DMG beacon frame bodycan hold several partly optional signaling fields and therefore itslength is variable. Thus, several options to signal a DD-A-BFT can bepossibly implemented:

-   -   Introduction of a simple DD-A-BFT control field with the        structure show in FIG. 10.    -   DD-A-BFT length field indicates the number of DD-A-BFT slots (1        up to 8).    -   FSS field indicates the number of SSW frame slots within one        DD-A-BFT slot (1 up to 16).    -   Next DD-A-BFT field indicates the number of BI during which the        DD-A-BFT is not present.    -   DD-A-BFT count field indicates the number of DD-A-BFTs since the        STA sending the DMG Beacon frame last switched RX DMG antennas        for a DD-A-BFT. A value of 0 indicates that the DMG antenna used        in the forthcoming DD-A-BFT differs from the DMG antenna used in        the last DD-A-BFT.    -   N-DD-A-BFT in Ant field indicates how many A-BFTs the STA        sending the DMG Beacon frame receives from each DMG antenna.    -   Introduction of an advanced DD-A-BFT control field (see FIG.        11), which enables the AP to use several DD-A-BFT phases to        train all receive sectors in case number of beams to be tested        is larger than the number of DD-A-BFT slots as signaled in        DD-A-BFT length field. This is indicated by ‘fragmented DD-A-BFT        bit. The number of required DD-A-BFT slots is indicated by        ‘DD-A-BFT span’.

If it is assumed that there is a total of N non-overlapping receivepatterns, each receive pattern can contribute a gain of roughly 10log₁₀N dB of link budget which results in √N fold link distanceaccording to the free space path loss formula for example.

Further if N different non-overlapping receive patterns are assumed,collision probability of STAs joining at same time can be reduced byfactor N, if STAs are assumed to be equally spatially distributed.

FIGS. 12-18 illustrate communication devices and methods according to asecond aspect of the present disclosure.

If STAs need to sweep the receive beams through each of sector sweep(SSW) slots with L RX beams (L being number of possible beams), this canbe a very large overhead, since all TX/RX combinations of directivebeams may have to be tested. If e.g. the AP listens directionally withall the beams which it has received during an initiator transmit sectorsweep (I-TXSS) phase, a large number of slots are necessary (currently amaximum of L=64 sweeps per antenna array are defined).

Thus, according to the second aspect, the set of first receive beamsutilized by the AP for listening in the beamforming training phasediffers from the set of third transmit beams utilized by the AP fortransmitting in the beacon transmission phase in number (only a subsetmay be necessary) and/or widths (larger beam widths may be used by theAP on receive) and/or angular sectors (the angular sectors can be acombination of sectors previously used for transmission in the beacontransmission phase).

The association beamforming training presented according to the secondaspect can be performed during similar A_BFT slots, as the DD-A-BFT asdescribed above or it can be alternatively performed in scheduledassociation beamforming service periods. A preferred embodiment impliesperforming the beamforming training in both DD-A-BFT and scheduledintervals to allow more flexibility and robustness, as will be describedfurther in this disclosure.

FIG. 12 shows a diagram of an embodiment of a beacon transmission phaseaccording to the second aspect. Similar to the above describedsolutions, the AP sends beacon frames 102 with directive beams 140(“third directive transmit beams”). In addition to what was previouslydescribed, each beacon frame 102 is embedded in a PPDU (physicalprotocol data unit) which has appended N_(r) training units (TRNs), i.e.in the embodiment shown in FIG. 12 a beacon PPDU 100 comprises preambleand header fields (PH) 101, a beacon frame 102 and one or more(generally N_(r)) training units 103. The STAs (only one is shown inFIG. 12) estimate link quality (e.g. by evaluating the received power)on one or more N_(r) Areceive beams 150 (“third receive beams”) for eachof the transmit beams 150 that contain TRN fields, and based on thisinformation they estimate the best wide beam on which they can transmitin a subsequent beamforming training phase.

According to the second aspect, in the association beamforming trainingphase, as e.g. shown in FIG. 13 for an embodiment, the AP may use forsome of the sectors wide beams 160 (“first receive beams”) correspondingto several of the narrow beams 140 that have been previously swept inthe beamforming transmission phase. More precisely, each angular sectoron which the AP receives during the association phase may comprise oneor a union of the angular sectors covered by narrow beams 140 in thebeamforming phase. To benefit from this, it is preferred for the STAs tohave some information about the correspondence between these narrowtransmit beams 140 used in the beacon transmission phase by the AP fortransmission and the wide receive beams 160 used in the beamformingtraining phase by the AP for listening. Several options are possible:

According to one option information about the correspondence between thenarrow transmit beams 140 and the wide receive beams 160 is contained inthe beacon 100. More clearly, in addition to the sector indexcorresponding to the directive transmit beam 140 (e.g., D₁ ^(i)) withwhich the frame is currently sent, each beacon frame 102 may contain theindex of the wide receive beam 160 to which the directive transmit beam140 corresponds (e.g., W₁ ^(i) where D₁ ^(i)∈W₁ ^(i)). If the directiveassociation can contain multiple sub-stages, in which different beamwidths can be used then each beacon frame 102 may contain all the widereceive beams 160 to which the narrow transmit beam 140 corresponds(e.g., W_(1,1) ^(i), . . . W_(S,1) ^(i), where D₁ ^(i)∈W_(S,1) ^(i)∈ . .. ∈W_(1,1) ^(i)).

The STA estimates the third receive beam 150, which is the mostappropriate (e.g., receives the strongest power) for the directivetransmit beam 140, on which the beacon 100 was sent. If the narrowtransmit beam 140 corresponds to only one wide sector, 160, as given bythe correspondence information, then in the association beamformingtraining phase the STA will send with a first transmit beam 170, in thetime slot in which the AP “listens” with this wide sector (i.e. with thewide first receive beam 160).

With respect to where this wide-narrow beam correspondence informationcan be included, two options are preferred: i) it can be in the (sectorsweep) SSW field, by reusing the RXSS bits which are reserved during thebeacon intervals, as shown in FIG. 14 or ii) it can be included in aninformation element of the beacon frame, e.g., in an extended schedule.

With respect to the third transmit beams 140 being used during each ofthe beacons 100, according to one option the same directive transmitbeam 140 may be used during the TRNs as has been used for the rest ofthe PPDU, as shown in FIG. 15 illustrating a diagram of a firstembodiment of a PPDU and frame structure and corresponding AWVconfigurations. Each STA finds the best third transmit beam D_(t) ^(i)and third receive beam 150 D_(1,j) ^(r) which maximize the receivedpower and will send in the association beamforming training phase with atransmit beam covering the same angular sector as D_(1,j) ^(r), in thetime interval allocated to AP reception with W₁ ^(i)

D₁ ^(i).

Alternatively, the AP may send during the beacon transmission phase inthe training intervals with a wide beam, with which it will receive inthe beamforming training phase, e.g., with W₁ ^(i) such that W₁ ^(i)

D₁ ^(i). To achieve this, one option is to allow the AP to change theAWV from directive D₁ ^(i) to wide W₁ ^(i)

D₁ ^(i), whereas the wide pattern W₁ ^(i) is only used for thetransmission of the TRN sequences. This allows the STAs to betterestimate the first transmit beams 170, which they may use in theassociation beamforming training phase to be best received by the AP.This is shown in FIG. 16 illustrating a diagram of a second embodimentof a PPDU and frame structure and corresponding AWV configurations

According to another option, a the AP may be allowed to transmit widebeams 141 on beacons intertwined with the narrow beams 142 and then havethe STAs infer the information about the narrow-wide correspondence fromthe behavior of the AP. This is shown in FIG. 17 illustrating a diagramof another embodiment of a beacon transmission phase. According to thisembodiment the AP sends after a certain number of narrow sweeps (i.e.with narrow third directive transmit beams 142) one frame 101 with thewide transmit beam 141 which will be ‘approximately’ used in thebeamforming training phase as first wide receive beam 160 (see FIG. 13).Contrary to the above described embodiment, the STAs only need toperform receive beam training during the time intervals corresponding tothe transmission with the wide beams, so that the training overhead canbe reduced, as training sequences do not need to be appended to all thebeacons, in particular the ones sent with narrow beams. This isindicated in FIG. 17 by the dashed lines for the TRN fields, thirdreceive beams 152 (which are optional) contrary to the mandatory TRNfields and third receive beams 151, respectively that are used fortraining and are marked with solid lines. Furthermore, these third widetransmit beams 141 may have extra training fields corresponding tonarrow third transmit beams 142 previously trained, therefore allowingthe STAs to gain information on the narrow-wide correspondence withoutadditional signaling fields. For this option, the Beacon element maystill contain the scheduling information i.e., the wide beam indexes, inthe order in which these will be used.

A further option considers implicit signaling depicted in FIG. 18illustrating a diagram of still another embodiment of a beacontransmission phase and a beamforming transmission phase. According tothis embodiment each beacon holds information about the length of thefurther stage or association phase (i.e. the beamforming trainingphase). This information about the length can be given in absolutemanner i.e., in number of slots M defined by the AP for association orrelative to the number of beacons N sent in the previous training (i.e.the beacon transmission phase) e.g., as an integer c=N/M. If there are Nbeacon frames transmitted each with a particular narrow beam 143, i.e. Nnarrow third transmit beams, then the AP sets M to an integer fractionalof N, (i.e. M·c=N with c being an integer with c≥1) and the AP listenswith a wide first receive beam 160 which combines c narrow beams 161,162. Thereby, the order of the beam sweep is kept unchanged with respectto the beacon transmission phase. For illustration it may be assumedthat N=4 and M=2 as well as beam indices n=1 . . . N and m=1 . . . M forbeacon transmission phase and association phase (beamforming trainingphase), respectively. An AP using implicit signaling would use for thefirst slot (m=1) a wide beam comprising beam n=1 and n=2 of beacontransmission phase, whereas in the second slot (m=2) the AP uses a widebeam combining beam n=3 and n=4. Since N and M are known by the STA fromthe beacon data c can be readily computed. Also a STA can determine theactual n in the beacon transmission phase where it receives the beaconwith best quality and by knowing c it can compute the value of m anddetermine when to transmit in the beamforming training phase. In thespecial case of c=1, the beams and their sequence are equal in thebeacon transmission phase and the beamforming training phase.

A further option to allow directive association beamforming trainingwith variable beam width, during A-BFT slots, is based on the concept ofusing a multiplier. This concept allows an increased number of A-BFTslots to be used by enhanced DMG (EDMG) stations. The number ofadditional slots is the value indicated in the A-BFT Length fieldmultiplied with the value in the Multiplier field, both defined in theEDMG beacon. Further, to allow only the EDMG STAs to access these slotsthe Duration field can be modified such that the DMG STAs “see” thebeginning of the A-BFT at a later time, i.e., after the enhanced A-BFTslots, therefore do not attempt access during modified association phasewhich they do not fully exploit. For directional association only theadditional A-BFT slots may be used, wherein the value of the multipliercan define “implicitly” the value of the beam width e.g., for amultiplier value of 2 the width of the angular sector is half of thewidth of an angular sector for multiplier 1.

In this case, within a beacon sent with a directive beam Di, the part ofthe RXSS Length field of the SSW field, which is currently reserved, canbe used to indicate the index of the A-BFT slot that the AP uses for anangular sector corresponding to the directive beam Di with which therespective frame is transmitted. Also, since this index only requires alimited number of bits, an additional field within the RXSS field may beused to indicate that the immediately following A-BFT is directive andthe following bits should be used for the directive A-BFT slotindication.

The disclosed signaling of wide beams and/or integration of wide beamswithin the transmit sector sweeps makes it possible to have a fullyflexible directive association phase. The AP may choose according to thelink conditions which sectors require a larger or finer resolution fordirective association and adapt the training phases to theseconci-tions. For example if collisions were detected within one sectoror if within one sector signals were detected but could not be properlydecoded, the directive association can be repeated using narrowerreceive beams. In this case the information about the receive beams mayonly be attached to narrow beams corresponding to these sectors.

The disclosed directive association phase may comprise one or moresub-stages. In the first sub-stage the STAs send one or more directivebeams, from the best ones that they have trained during the beacontransmission phase, while the AP receives directionally with beams,which may differ in pattern to the narrow transmit beams used in theprevious I-TXSS phase, which however correspond to the schedulingannounced. In the example shown in FIG. 13, the AP uses wide transmitbeams 160 W₁ ^(i), where each wide beam 150 covers an angular sectorsimilar to the combination of the angular sectors covered by thecombination of the third receive sectors D₁ ^(i) and D₂ ^(i) used in thebeamforming transmission phase (see FIG. 12).

An optional feedback stage may be beneficial inside this period. In thiscase, after each stage of wide beam width reception, the AP sends back afeedback message 104 to the STAs from which it has received a message toprevent them from reattempting association and interfering others. Afterthe feedback stage, the training may resume with an additionalsub-stage, in which the third receive beams 160 are narrower than in theprevious sub-stage, or more time slots are allowed. A mandatory feedbackstage should be present after the last such sub-stage to allow the AP tosend to all STAs whose frames it has decoded an acknowledgment 103 thatassociation was successful. Should optional feedback be allowed, thenthe beacon should include as an extended schedule the sequence of beamsthat it uses and indicate that a feedback stage is present.

For transmitting feedback to one particular STA in the (optional ormandatory) feedback stage a second transmit beam 163 is used by the AP,which may optionally correspond to the third transmit beam 140 selectedby the STA as best third transmit beam in the beacon transmission phase.Alternatively, the AP may aggregate multiple feedbacks to multiple STAswithin one wide sector, in which case this will transmit the feedbackwith the wide beam covering the angular sectors corresponding to thebest third transmit beams received by the receptive STAs. Yet anotheroption, in the case when multiple STAs have been received during anassociation slot with wide beam, is to allow the AP to schedule multipletime slots in which it sends the feedback individually to each of theseSTAs, with the narrow third transmit beam, reported by each of theseSTAs. During the feedback stages the STAs listen using a second receivebeam 171, 181, which may correspond to the best third receive beamselected by the respective STA in the beacon transmission phase.

As simple signaling option is to have indicate in the extended schedule,in which allocations the STAs should expect the feedback information,whereas the wide-narrow indication corresponding to each sub-stage canbe included in a beacon element. A different possibility is that severalservice periods can be scheduled i.e., each sub-stage as described abovecorresponds to one separate training period.

The optional feedback may be useful also in the case when the AP listenssequentially with various antennas. This is because there may be casesin which a STA hears the signal from multiple antennas, thus mayreattempt transmission on the best sector of a different antenna, shouldit have not received any feedback/acknowledgement from the previousantenna.

According to a further embodiment modifications may be made to the STAbehavior. For instance, in long range or blockage scenarios the STAs maynot be able to hear the beacons omni-directionally and therefore may notmanage to figure out that TRNs are attached to certain frames to allowreceive beam training. In such cases, these STAs may listen with somewide receive beams over one or more beacon intervals and may possiblyreduce the beam width e.g., once signals are detected in a sector, beamscan be narrowed to allow for packet detection and further narrowedduring the TRN fields to allow for the best estimation of beams to beused for the transmission in the association phase. For such long rangecases, to compensate for the low link budget in uplink, during theassod-ation several time slots can be randomly chosen, in which the STAsmay sweep narrow beams within the receive sector, estimated during thetransmit sector. For such cases STAs may feedback a long range flag, tolet the AP know that only double directive transmissions are possibleand adapt various procedures that generally require omni-directionaltransmission in one side (e.g., RTS/CTS). Whenever multiple allocationsfor the same receive beams are allocated, the STAs may transmit withseveral narrow beams from the sector which was considered the best forreception.

According to a further embodiment modifications may be made to thescheduling element. The scheduling element can be within beacon frames,thus sent during the beacon interval or it can be within announceframes, thus sent during association time intervals. The second optionallows the AP to decide upon the receive beams to be used in anadditional scheduled directive association phase, based on the outcomeof a regular A. BFT or a directive DD-A-BFT. The advantage of the latteroption is larger flexibility at the AP, which may allow e.g., onlyseveral problematic sectors to be tested, where e.g., collisions weredetected. A scheduling element within each beacon frame or within eachannounce frame may contain allocation information for all the sub-stagesof the directive association described above. Two types of allocationmay exist: a first one to specify the allocation intervals in which theAP listens directively while STAs are allowed to access the channel, anda second one of allocation intervals in which the STAs are in listeningmode to receive acknowledgment from the AP, should the AP have heardthem. Each of the former types of allocations may contain a beamformingcontrol field, which specifies the index of the wide beam which is usedin the specific allocation. This can be e.g. done by reusing thereserved bits within the current Beamforming Control field. Further,this field may contain a field indicating the number of SSW frames thatmay be used by a STA. Whenever the value inside this field is above 0,the STAs may sweep inside the best receive wide beam sector to increasethe chances to be received by the AP. This information can be e.g.included in the Beamforming Control field by reusing the RXSS lengthfield. The allocation type defining these allocation intervals may needto be newly defined to respect at the same time legacy and the newrequirements, mentioned above, however this can be easily done as thereexist reserved bits for the allocation type in current allocation field(sometimes also called AID field) structure definition. An example of ascheduling element is shown in FIG. 19. Here, the allocation fields areindicated as AID 1, AID 2, etc. since each allocation field is generallyindicated by a corresponding allocation identifier (AID).

In an alternative embodiment each of the beacon frames or announceframes contains only scheduling information indicating the allocationintervals that are related to the directive third receive beam withwhich the respective beams have been received, i.e. if the beacon framehas been transmitted with directive beam D₁ ^(i) the scheduling elementwill contain an allocation with a beamforming control informationspecifying the index of the wide beam W₁ ^(i) such that D₁ ^(i)∈W₁ ^(i)and an allocation for the feedback/ack. Optionally allocation fields forintervals where AP listens with narrower beam than W₁ ^(i) but widerthan W₁ ^(i) may be specified.

According to a preferred embodiment, after the beacon transmission phaseis performed as described above, a directive association beamformingtraining interval (D-ABFT) is allowed, in which the AP listens withcoarse beams W₁ ^(i), . . . , W_(N) _(s) ^(i), wherein each W₁ ^(i)corresponds to some of the directive sectors swept within the beacontransmission phase. Hereby, N_(S) represents the number of A-BFT slotsas specified by the beacon. As the succession of the first wide receivebeams follows the same order as the third narrow transmit beams, thereis one coarse beam per A-BFT slot and the coarse beam (first widereceive beam) covers the wide angular domain as the superposition of allnarrow third transmit beams swept during the beacon transmission phase.The presence of the directive A-BFT can be indicated in beacons and mayonly be accessed by EDMG STAs. The mechanisms of the A-BFT are respectedin the sense that STAs are allowed to access one or more of the widebeams, but only for the slots in which the receive beams employed at theAP correspond to the best received beam of the STA. If after theDD-A-BFT, collisions were detected in some of the sectors, the AP maysend within the ATI a scheduling element as described, whereinallocation intervals are assigned for the problematic sectors i.e. withindications of the wide beams or possibly narrower beams within the widebeam.

FIG. 20 shows a diagram of another embodiment of an extended schedulingelement, wherein allocations are defined such as to allow the AP toreceive simultaneously with more than one directive beam. Assuming onewide beam that is used for reception can be approximated by asuperposition of several narrower beams, that have been used during theBTI beam sweep (i.e. in the beacon transmission phase), an easy wayexists to signal with which variable beamwidth the AP listens during theassociation phase (i.e. the beamforming training phase). This can bebasically done by scheduling allocations with multiple narrow beamreception having the same allocation time. Each allocation field thusindicates a directive beam D and its time of use vTSF. Here, TSF standsfor the timing synchronization function and vTSF represents the lower 4octets of the TSF at the time the SP (service period, i.e. the period ofdata transmission) starts. For example, the Allocation 1 indicates thetime vTSF₁ when the first directive beam D₁ ^(i) (which may e.g. be thebeam 161 in FIG. 18) is used. Since the Allocation 2 field has the samestart time vTSF₁ as Allocation 1, however a different directive beam D₁^(i), this has a similar effect to receiving at the start time vTSF₁with a wide beam W₁ ^(i) covering a sector composed of the two sectorsdefined by D₁ ^(i) and D₂ ^(i).

The allocations are generally defined after the STAs are associated withan AP and therefore have already received an association ID. Theseassociation IDs are then utilized to indicate which STAs will transmitwithin a specific allocation. Two values may be used: A first valueindicates broadcast (i.e., if source association ID=broadcast ID allSTAs may transmit in the specific allocation, if destination associationID=broadcast ID, all STAs are in reception mode). A second valueindicates AP (i.e., if source association ID=AP association ID, then theAP is the one transmitting in the respective association). Hence, the“allocations” shown in FIG. 20 may comprise two further entriesrepresenting these two values.

For the particular case of directive association during DTI, suchassociation IDs are not yet available. Furthermore allowing the use ofthe broadcast association ID would confuse legacy STAs which maytransmit within this particular allocation and thus interfere with theassociation. Therefore, in an embodiment a specific broadcastassociation ID is defined and reserved, which can be only understood bythe EDMG STAs or the DMG STAs which are able to participate in this typeof training.

The number of spatial allocations, i.e., number of time blocks in whichan AP listens with a particular RX beam, can be defined within theallocation frame, e.g. by reusing the NBlks field, which indicates thenumber of the SSW frames (i.e. the number of available SSW transmitopportunities). The maximum number of space time slots (N_STS) in whicha STA may transmit during an allocation i.e., the number of transmitbeams that the STA may sweep, can be defined in the BF Control field ofthe DMG extended schedule eb-ment or in the EDMG extended scheduleelement of this allocation. In the first case either the RXSS Length maybe reused, so that basically the STAs reinterpret this as N_STS, orreserved bits in this field may be used to encode N_STS. In the secondcase, several reserved bits of the EDMG extended schedule element can beused to encode N_STS.

FIG. 21 shows an exemplary modification of the EDMG extended scheduleelement. The Allocation Key comprises the number of NBIk, i.e. thenumber of available SSW frames and N_STS indicates how many SSW framesmay be used. Two bits are designated to signal the maximum number ofspace time slots in which a STA can transmit. Either a linear or anexponential interpretation of this field may be applied as illustratedin the following table:

N_STS value Actual N_STS Actual N_STS in field value (linear) value(exponential) 00 1 1 01 2 2 10 3 4 11 4 8

In still another embodiment an additional field (in the allocationfields shown in FIGS. 19 and 20) to signal the gain of the beams D_(j)^(r) or W_(j) ^(r) or a function depending on the gain of the beamsD_(j) ^(r) or W_(j) ^(r) may be provided, which can enable the STAs tocompute if the link budget is enough for them to access the beamformedSP, in which the AP listens with the RX beam D_(j) ^(r) or W_(j) ^(r):

By use of communication devices and methods according to the presentdisclosure several advantages can be achieved. In particular: long rangeAP discovery for mmWave systems; increase of roughly 10 log₁₀ M dB inlink budget in association phase; improved channel access in case ofreciprocity; and spatial reuse in association phase, i.e. spatial beamproperties are exploited for association phase

Further, according to the second aspect, the set of first receive beamsutilized by the AP for listening in the beamforming training phasediffers from the set of third transmit beams utilized by the AP fortransmitting in the beacon transmission phase in number (only a subsetmay be necessary) and/or widths (larger beam widths may be used by theAP on receive) and/or angular sectors (the angular sectors can be acombination of sectors previously used for transmission in the beacontransmission phase).

Using beams with variable beam widths during the beacon transmissionphase and the association phase, as described above for the secondaspect, can reduce the association time and/or the total beam trainingtime, while keeping the advantages of the directive associationsolutions, in particular low collision and long range. Based on themethod and signaling described for the second aspect a more flexibleassociation phase is possible, which is adapted to specific scenarios(e.g., collisions happening preponderantly in some angular sectors).

Thus, the foregoing discussion discloses and describes merely exemplaryembodiments of the present disclosure. As will be understood by thoseskilled in the art, the present disclosure may be embodied in otherspecific forms without departing from the spirit or essentialcharacteristics thereof. Accordingly, the disclosure of the presentdisclosure is intended to be illustrative, but not limiting of the scopeof the disclosure, as well as other claims. The disclosure, includingany readily discernible variants of the teachings herein, defines, inpart, the scope of the foregoing claim terminology such that noinventive subject matter is dedicated to the public.

In the claims, the word “comprising” does not exclude other elements orsteps, and the indefinite article “a” or “an” does not exclude aplurality. A single element or other unit may fulfill the functions ofseveral items recited in the claims. The mere fact that certain measuresare recited in mutually different dependent claims does not indicatethat a combination of these measures cannot be used to advantage.

In so far as embodiments of the disclosure have been described as beingimplemented, at least in part, by software-controlled data processingapparatus, it will be appreciated that a non-transitory machine-readablemedium carrying such software, such as an optical disk, a magnetic disk,semiconductor memory or the like, is also considered to represent anembodiment of the present disclosure. Further, such a software may alsobe distributed in other forms, such as via the Internet or other wiredor wireless telecommunication systems.

The elements of the disclosed devices, apparatus and systems may beimplemented by corresponding hardware and/or software elements, forinstance appropriated circuits. A circuit is a structural assemblage ofelectronic components including conventional circuit elements,integrated circuits including application specific integrated circuits,standard integrated circuits, application specific standard products,and field programmable gate arrays. Further a circuit includes centralprocessing units, graphics processing units, and microprocessors whichare programmed or configured according to software code. A circuit doesnot include pure software, although a circuit includes theabove-described hardware executing software.

It follows a list of further embodiments of the disclosed subjectmatter:

1. A communication device (2) for RF-based communication with anothercommunication device (1), said communication device comprising:

-   -   antenna circuitry configured to transmit and receive RF signals,        and    -   beamforming circuitry configured to perform beamforming and to        control the antenna circuitry to transmit data, in a beacon        transmission phase prior to the beamforming training phase,        using a set of third directive transmit beams in subsequent time        slots and to listen, in the beamforming training phase, using a        set of first directive receive beams in subsequent time slots        that is different from the set of third directive transmit        beams.

2. The communication device as defined in any preceding embodiment,

wherein the beamforming circuitry is configured to control the antennacircuitry to listen using different first directive receive beams insubsequent time slots, wherein one or more of the first directive beamshave a larger beam width and/or are covering different angular sectorsand/or are only a subset of the third directive transmit beams used inthe beacon transmission phase for transmitting data.

3. The communication device as defined in embodiment 2,

wherein the beamforming circuitry is configured to control the antennacircuitry to adapt the beam width and/or the angular sectors and/or thenumber of the first directive receive beams used in subsequent timeslots.

4. The communication device as defined in any preceding embodiment,

wherein the beamforming circuitry is configured to control the antennacircuitry to transmit scheduling information in the beacon transmissionphase, said scheduling information indicating in which time slot whichfirst directive receive beam will be used by the communication devicefor listening in the beamforming training phase and/or indicating if thecommunication device is transmitting in a certain time slot and/or whichother communication device is allowed to transmit in a certain timeslot.

5. The communication device as defined in any preceding embodiment,

wherein the beamforming circuitry is configured to control the antennacircuitry to transmit correspondence information in the beacontransmission phase, said correspondence information indicating thecorrespondence between a third transmit beam used by the communicationdevice in the beacon transmission phase for transmitting data in aparticular time slot and a first receive beam used by the communicationdevice in the beamforming training phase for listening in a particulartime slot.

6. The communication device as defined in any preceding embodiment,

wherein the beamforming circuitry is configured to control the antennacircuitry to select a sequence of narrow and wide third transmit beamsused for transmitting data in the beacon transmission phase allowing theother communication device to determine in which time slot to transmitdata with a selected first transmit beam.

7. The communication device as defined in any preceding embodiment,

wherein the beamforming circuitry is configured to control the antennacircuitry to transmit data in the beacon transmission phase in dataunits, a data unit comprising a beacon frame and one or more trainingunits, wherein a beacon frame of a data unit is transmitted using anarrower third transmit beam than the one or more training units of thedata unit.

8. A communication method for RF-based communication with anothercommunication device, said communication method controlling an antennacircuitry to perform beamforming and to transmit data, in a beacontransmission phase prior to the beamforming training phase, using a setof third directive transmit beams in subsequent time slots and tolisten, in the beamforming training phase, using a set of firstdirective receive beams in subsequent time slots that is different fromthe set of third directive transmit beams.

9. A communication device (1) for RF-based communication with anothercommunication device (2), said communication device comprising:

-   -   antenna circuitry configured to transmit and receive RF signals,        and    -   beamforming circuitry configured to perform beamforming and to        control the antenna circuitry to transmit data using at least        one first directive transmit beam while the other communication        device is listening subsequently using different first directive        receive beams, wherein data is only transmitted in one or more        selected time slots, in which the other communication device is        listening with a selected first directive receive beam, wherein        the one or more time slots are selected based on information        received from the other communication device or derived from        third directive transmit beams used by the other communication        device to transmit data in a beacon transmission phase prior to        the beamforming training phase.

10. The communication device as defined in embodiment 9,

wherein the beamforming circuitry is configured to control the antennacircuitry to carry out, in the beacon transmission phase, the steps of

a) listening using different third directive receive beams in at leastpart of a time slot while the other communication device transmits datausing a third directive transmit beam, wherein the other communicationdevice transmits data using different third directive transmit beams insubsequent time slots, and

b) selecting one or more third directive receive beams for use indetermining the first directive transmit beams to be used in thesubsequent beamforming training phase.

11. The communication device as defined in embodiment 9, wherein thebeamforming circuitry is configured to control the antenna circuitry tocarry out, in the beacon transmission phase, the steps of

a) listening using a quasi-omnidirectional receive beam in at least partof a time slot while the other communication device transmits data usinga third directive transmit beam, wherein the other communication devicetransmits data using different third directive transmit beams insubsequent time slots, and

b) selecting one or more third directive transmit beams for use indetermining in which one or more time slots to transmit data in thebeamforming training phase by determining when the other communicationdevice listens with a first directive receive beam corresponding to orcovering a selected third directive transmit beam.

12. The communication device as defined in embodiment 9,

wherein the beamforming circuitry is configured to control the antennacircuitry to select the one or more time slots in which it transmitsdata in the beamforming training phase based on scheduling informationreceived from the other communication device in a beacon transmissionphase prior to the beamforming training phase, said schedulinginformation indicating in which time slot which first directive receivebeam will be used by the other communication device for listening in thebeamforming training phase and/or indicating if the other communicationdevice is transmitting in a certain time slot and/or if thecommunication device is allowed to transmit in a certain time slot.

13. The communication device as defined in embodiment 9,

wherein the beamforming circuitry is configured to control the antennacircuitry to select the one or more time slots in which it transmitsdata in the beamforming training phase based on correspondenceinformation received from the other communication device in a beacontransmission phase prior to the beamforming training phase, saidcorrespondence information indicating the correspondence between a thirdtransmit beam used by the other communication device in the beacontransmission phase for transmitting data in a particular time slot and afirst receive beam to be used by the other communication device in thebeamforming training phase for listening in a particular time slot.

14. The communication device as defined in embodiment 12 and/or 13,

wherein the beamforming circuitry is configured to derive the schedulinginformation and/or the correspondence information from an SSW field or abeamforming control field or an information field of a beacon frametransmitted by the other communication device in the beacon transmissionphase.

15. The communication device as defined in embodiment 9,

wherein the beamforming circuitry is configured to control the antennacircuitry to select the one or more time slots in which it transmitsdata in the beamforming training phase based on the sequence in whichthe other communication device transmits data with different thirdtransmit beams in a beacon transmission phase prior to the beamformingtraining phase, wherein two or more third transmit beams covered by asingle first receive beam that will be used by the other communicationdevice in the beamforming training phase are followed or preceded by athird transmit beam corresponding to said first receive beam.

16. The communication device as defined in embodiment 9,

wherein the beamforming circuitry is configured to control the antennacircuitry to select the one or more time slots in which it transmitsdata in the beamforming training phase based on the sequence in whichthe other communication device transmits data with different thirdtransmit beams in the beacon transmission phase, wherein a predeterminednumber of subsequently used third transmit beams will be covered by afirst receive beam and/or wherein the sequence of first receive beamscorresponds to the sequence of third transmit beams.

17. The communication device as defined in embodiment 9,

wherein the beamforming circuitry is configured to control the antennacircuitry to listen, after one or more time slots of transmitting dataor in specially allocated feedback intervals, using a second receivebeam for a response from the other communication device, which isconfigured to transmit, if the data transmitted by the communicationdevice have been received, a response using a second directive transmitbeam.

18. The communication device as defined in embodiment 17,

wherein the beamforming circuitry is configured to control the antennacircuitry to include a second transmit beam information in the datatransmitted using at least one first directive transmit beam for use bythe other communication device for transmitting the response by a seconddirective transmit beam indicated by the second transmit beaminformation.

19. A communication method for RF-based communication with anothercommunication device, said communication method controlling an antennacircuitry to perform beamforming and in a beamforming training phase totransmit data using at least one first directive transmit beam while theother communication device is listening subsequently using differentfirst directive receive beams, wherein data is only transmitted in oneor more selected time slots, in which the other communication device islistening with a selected first directive receive beam, wherein the oneor more time slots are selected based on information received from theother communication device or derived from third directive transmitbeams used by the other communication device to transmit data in abeacon transmission phase prior to the beamforming training phase.

20. A non-transitory computer-readable recording medium that storestherein a computer program product, which, when executed by a processor,causes the method according to embodiment 8 or 19 to be performed.

21. A computer program comprising program code means for causing acomputer to perform the steps of said method according to embodiment 8or 19 when said computer program is carried out on a computer.

A1. A communication device (1) for RF-based communication with anothercommunication device (2), said communication device (1) comprising:

-   -   an antenna circuitry (10) configured to transmit and receive RF        signals, and    -   a beamforming circuitry (11) configured to perform beamforming        and to control the antenna circuitry in a beamforming training        phase to transmit and/or receive RF signals using one or more        selected directive beams, wherein the beamforming cir-circuitry        (11) is configured to perform beamforming training by        controlling the antenna circuitry    -   i) to transmit data using at least one first directive transmit        beam, wherein the other communication device (2) is configured        to listen using a first directive receive beam, said data        including a second transmit beam information,    -   ii) to subsequently listen using a predetermined second        directive receive beam for a response from the other        communication device (2), which is configured to transmit, if        the data transmitted in step i) have been received, a response        using a second directive transmit beam indicated by the second        transmit beam information, and    -   iii) to repeat steps i) and ii) if no response is received in        step ii).        A2. The communication device as defined in embodiment A1,        wherein the beamforming circuitry (11) is configured to control        the antenna circuitry to successively transmit the data in        step i) with a number of different first directive transmit        beams.        A3. The communication device as defined in embodiment A2,        wherein the beamforming circuitry (11) is configured to control        the antenna circuitry to transmit a predefined number of first        directive beams as signaled by the other communication device in        a previous training phase or a beacon transmission phase.        A4. The communication device as defined in embodiment A2 or A3,        wherein the beamforming circuitry (11) is configured to obtain        from the response received in step ii) a first transmit beam        information indicating at least one of the first directive        transmit beams by which the data, which have been received by        the second communication device (2), have been transmitted by        the communication device (1).        A5. The communication device as defined in any one of the        preceding embodiments A,        wherein the beamforming circuitry (11) is configured to control        the antenna circuitry to transmit the data in step i) with a        single first directive transmit beam.        A6. The communication device as defined in embodiment A5,        wherein the beamforming circuitry (11) is configured to control        the antenna circuitry to transmit the data in step i) with the        same or different single first directive transmit beams in        subsequent iterations of step i).        A7. The communication device as defined in embodiment A5 or A6,        wherein the beamforming circuitry (11) is configured to control        the antenna circuitry to use the same beam as first directive        transmit beam and second directive receive beam.        A8. The communication device as defined in any one of the        preceding embodiments A,        wherein the beamforming circuitry (11) is configured to decide        in step ii) that a response has been received if it includes a        first identifier of the communication device (1).        A9. The communication device as defined in any one of the        preceding embodiments A,        wherein the beamforming circuitry (11) is configured to control        the antenna circuitry to carry out, in a beacon transmission        phase prior to the beamforming training phase, the steps of        a) listening using a third receive beam while the other        communication device (2) transmits a second identifier of the        other communication device (2) subsequently using different        third directive transmit beams, and        b) setting, once the second identifier has been received, the        third directive transmit beam used for transmitting the second        identifier as second directive transmit beam indicated by the        second transmit beam information.        A10. The communication device as defined in embodiment A9,        wherein the beamforming circuitry (11) is configured to control        the antenna circuitry    -   to listen, in step a), by successively using different third        directive receive beams, while in each succession the other        communication device (2) subsequently uses different third        directive transmit beams and    -   by setting, in step b), the third directive receive beam with        which the second identifier has been received, as second        directive receive beam.        A11. A communication method for RF-based communication with        another communication device (2), said communication method        controlling an antenna circuitry in a beamforming training phase        to transmit and/or receive RF signals using one or more selected        directive beams by

-   i) transmitting data using at least one first directive transmit    beam, wherein the other communication device (2) is configured to    listen using a first directive receive beam, said data including a    second transmit beam information,

-   ii) subsequently listening using a predetermined second directive    receive beam for a response from the other communication device (2),    which is configured to transmit, if the data transmitted in step i)    have been received, a response using a second directive transmit    beam indicated by the second transmit beam information, and

-   iii) repeating steps i) and ii) if no response is received in step    ii).    A12. A communication device (2) for RF-based communication with    another communication device (1), said communication device (2)    comprising:    -   an antenna circuitry (20) configured to transmit and receive RF        signals, and    -   a beamforming circuitry (21) configured to perform beamforming        and to control the antenna circuitry, in a beamforming training        phase, to transmit and/or receive RF signals using one or more        selected directive beams, wherein the beamforming circuitry (21)        is configured to perform beamforming training by controlling the        antenna circuitry    -   i) to listen using a first directive receive beam for data        transmitted by the other communication device (1) using at least        one first directive transmit beam, said data including a second        transmit beam information,    -   ii) to subsequently transmit, if the data transmitted in step i)        have been received, a response using a second directive transmit        beam indicated by the second transmit beam information, wherein        the other communication device (1) is configured to listen using        a predetermined second directive receive beam, and    -   iii) to repeat steps i) and ii) by using different first        predetermined directive receive beams in step i).        A13. The communication device as defined in embodiment A12,        wherein the beamforming circuitry (21) is configured to include        in the response a first transmit beam information indicating the        first directive transmit beam by which the data, which have been        received by the communication device (2), have been transmitted        by the other communication device (1).        A14. The communication device as defined in embodiment A12 or        A13,        wherein the beamforming circuitry (21) is configured to control        the antenna circuitry to include in the response a first        identifier of the other communication device (1) from which the        data have been received.        A15. The communication device as defined in embodiment A14,        wherein the beamforming circuitry (21) is configured to control        the antenna circuitry to include in the response a first        identifier of another communication device from which the data        have been received with highest quality or SNR.        16. The communication device as defined in any one of the        embodiments A12 to A15,        wherein the beamforming circuitry (21) is configured to control        the antenna circuitry to transmit a response only if data have        been received in step i) with a quality or SNR above a        predetermined threshold.        A17. The communication device as defined in any one of the        embodiments A12 to A15,        wherein the beamforming circuitry (21) is configured to control        the antenna circuitry to perform beacon transmission, prior to        beamforming training, by transmitting a second identifier of the        second communication device (2) subsequently using different        third directive transmit beams, while the other communication        device (1) is configured to listen using a third receive beam.        A18. The communication device as defined in any one of the        embodiments A12 to A15,        wherein the beamforming circuitry (21) is configured to maintain        an ordered list of other communication devices and their        respective first transmit beam information from which data have        successfully been received and/or wherein the beamforming        circuitry (21) is configured to control the antenna circuitry to        include in the response one identifier and first transmit beam        information of the ordered list while removing this data from        the ordered list.        A19. A communication method for RF-based communication with        another communication device (1), said communication method        controlling an antenna circuitry, in a beamforming training        phase, to transmit and/or receive RF signals using one or more        selected directive beams by        i) listening using a first directive receive beam for data        transmitted by the other communication device (1) using at least        one first directive transmit beam, said data including a second        transmit beam information,        ii) subsequently transmitting, if the data transmitted in        step i) have been received, a response using a second directive        transmit beam indicated by the second transmit beam information,        wherein the other communication device (1) is configured to        listen using a predetermined second directive receive beam, and        iii) repeating steps i) and ii) by using different first        predetermined directive receive beams in step i).        A20. A non-transitory computer-readable recording medium that        stores therein a computer program product, which, when executed        by a processor, causes the method according to embodiment A11 or        A19 to be performed.        A21. A computer program comprising program code means for        causing a computer to perform the steps of said method according        to embodiment A11 or A19 when said computer program is carried        out on a computer.

1. A communication device for RF-based communication with anothercommunication device, said communication device comprising: antennacircuitry configured to transmit and receive RF signals, and beamformingcircuitry configured to perform beamforming and to control the antennacircuitry to transmit data, in a beacon transmission phase prior to thebeamforming training phase, using a set of third directive transmitbeams in subsequent time slots and to listen, in the beamformingtraining phase, using a set of first directive receive beams insubsequent time slots that is different from the set of third directivetransmit beams.
 2. The communication device as claimed in claim 1,wherein the beamforming circuitry is configured to control the antennacircuitry to listen using different first directive receive beams insubsequent time slots, wherein one or more of the first directive beamshave a larger beam width and/or are covering different angular sectorsand/or are only a subset of the third directive transmit beams used inthe beacon transmission phase for transmitting data.
 3. Thecommunication device as claimed in claim 2, wherein the beamformingcircuitry is configured to control the antenna circuitry to adapt thebeam width and/or the angular sectors and/or the number of the firstdirective receive beams used in subsequent time slots.
 4. Thecommunication device as claimed in claim 1, wherein the beamformingcircuitry is configured to control the antenna circuitry to transmitscheduling information in the beacon transmission phase, said schedulinginformation indicating in which time slot which first directive receivebeam will be used by the communication device for listening in thebeamforming training phase and/or indicating if the communication deviceis transmitting in a certain time slot and/or which other communicationdevice is allowed to transmit in a certain time slot.
 5. Thecommunication device as claimed in claim 1, wherein the beamformingcircuitry is configured to control the antenna circuitry to transmitcorrespondence information in the beacon transmission phase, saidcorrespondence information indicating the correspondence between a thirdtransmit beam used by the communication device in the beacontransmission phase for transmitting data in a particular time slot and afirst receive beam used by the communication device in the beamformingtraining phase for listening in a particular time slot.
 6. Thecommunication device as claimed in claim 1, wherein the beamformingcircuitry is configured to control the antenna circuitry to select asequence of narrow and wide third transmit beams used for transmittingdata in the beacon transmission phase allowing the other communicationdevice to determine in which time slot to transmit data with a selectedfirst transmit beam.
 7. The communication device as claimed in claim 1,wherein the beamforming circuitry is configured to control the antennacircuitry to transmit data in the beacon transmission phase in dataunits, a data unit comprising a beacon frame and one or more trainingunits, wherein a beacon frame of a data unit is transmitted using anarrower third transmit beam than the one or more training units of thedata unit.
 8. A communication method for RF-based communication withanother communication device, said communication method controlling anantenna circuitry to perform beamforming and to transmit data, in abeacon transmission phase prior to the beamforming training phase, usinga set of third directive transmit beams in subsequent time slots and tolisten, in the beamforming training phase, using a set of firstdirective receive beams in subsequent time slots that is different fromthe set of third directive transmit beams.
 9. A communication device forRF-based communication with another communication device, saidcommunication device comprising: antenna circuitry configured totransmit and receive RF signals, and beamforming circuitry configured toperform beamforming and to control the antenna circuitry to transmitdata using at least one first directive transmit beam while the othercommunication device is listening subsequently using different firstdirective receive beams, wherein data is only transmitted in one or moreselected time slots, in which the other communication device islistening with a selected first directive receive beam, wherein the oneor more time slots are selected based on information received from theother communication device or derived from third directive transmitbeams used by the other communication device to transmit data in abeacon transmission phase prior to the beamforming training phase. 10.The communication device as claimed in claim 9, wherein the beamformingcircuitry is configured to control the antenna circuitry to carry out,in the beacon transmission phase, the steps of a) listening usingdifferent third directive receive beams in at least part of a time slotwhile the other communication device transmits data using a thirddirective transmit beam, wherein the other communication devicetransmits data using different third directive transmit beams insubsequent time slots, and b) selecting one or more third directivereceive beams for use in determining the first directive transmit beamsto be used in the subsequent beamforming training phase.
 11. Thecommunication device as claimed in claim 9, wherein the beamformingcircuitry is configured to control the antenna circuitry to carry out,in the beacon transmission phase, the steps of a) listening using aquasi-omnidirectional receive beam in at least part of a time slot whilethe other communication device transmits data using a third directivetransmit beam, wherein the other communication device transmits datausing different third directive transmit beams in subsequent time slots,and b) selecting one or more third directive transmit beams for use indetermining in which one or more time slots to transmit data in thebeamforming training phase by determining when the other communicationdevice listens with a first directive receive beam corresponding to orcovering a selected third directive transmit beam.
 12. The communicationdevice as claimed in claim 9, wherein the beamforming circuitry isconfigured to control the antenna circuitry to select the one or moretime slots in which it transmits data in the beamforming training phasebased on scheduling information received from the other communicationdevice in a beacon transmission phase prior to the beamforming trainingphase, said scheduling information indicating in which time slot whichfirst directive receive beam will be used by the other communicationdevice for listening in the beamforming training phase and/or indicatingif the other communication device is transmitting in a certain time slotand/or if the communication device is allowed to transmit in a certaintime slot.
 13. The communication device as claimed in claim 9, whereinthe beamforming circuitry is configured to control the antenna circuitryto select the one or more time slots in which it transmits data in thebeamforming training phase based on correspondence information receivedfrom the other communication device in a beacon transmission phase priorto the beamforming training phase, said correspondence informationindicating the correspondence between a third transmit beam used by theother communication device in the beacon transmission phase fortransmitting data in a particular time slot and a first receive beam tobe used by the other communication device in the beamforming trainingphase for listening in a particular time slot.
 14. The communicationdevice as claimed in claim 12, wherein the beamforming circuitry isconfigured to derive the scheduling information and/or thecorrespondence information from an SSW field or a beamforming controlfield or an information field of a beacon frame transmitted by the othercommunication device in the beacon transmission phase.
 15. Thecommunication device as claimed in claim 9, wherein the beamformingcircuitry is configured to control the antenna circuitry to select theone or more time slots in which it transmits data in the beamformingtraining phase based on the sequence in which the other communicationdevice transmits data with different third transmit beams in a beacontransmission phase prior to the beamforming training phase, wherein twoor more third transmit beams covered by a single first receive beam thatwill be used by the other communication device in the beamformingtraining phase are followed or preceded by a third transmit beamcorresponding to said first receive beam.
 16. The communication deviceas claimed in claim 9, wherein the beamforming circuitry is configuredto control the antenna circuitry to select the one or more time slots inwhich it transmits data in the beamforming training phase based on thesequence in which the other communication device transmits data withdifferent third transmit beams in the beacon transmission phase, whereina predetermined number of subsequently used third transmit beams will becovered by a first receive beam and/or wherein the sequence of firstreceive beams corresponds to the sequence of third transmit beams. 17.The communication device as claimed in claim 9, wherein the beamformingcircuitry is configured to control the antenna circuitry to listen,after one or more time slots of transmitting data or in speciallyallocated feedback intervals, using a second receive beam for a responsefrom the other communication device, which is configured to transmit, ifthe data transmitted by the communication device have been received, aresponse using a second directive transmit beam.
 18. The communicationdevice as claimed in claim 17, wherein the beamforming circuitry isconfigured to control the antenna circuitry to include a second transmitbeam information in the data transmitted using at least one firstdirective transmit beam for use by the other communication device fortransmitting the response by a second directive transmit beam indicatedby the second transmit beam information.
 19. A communication method forRF-based communication with another communication device, saidcommunication method controlling an antenna circuitry to performbeamforming and in a beamforming training phase to transmit data usingat least one first directive transmit beam while the other communicationdevice is listening subsequently using different first directive receivebeams, wherein data is only transmitted in one or more selected timeslots, in which the other communication device is listening with aselected first directive receive beam, wherein the one or more timeslots are selected based on information received from the othercommunication device or derived from third directive transmit beams usedby the other communication device to transmit data in a beacontransmission phase prior to the beamforming training phase.
 20. Anon-transitory computer-readable recording medium that stores therein acomputer program product, which, when executed by a processor, causesthe method according to claim 8 to be performed.